Photolithography is one of the most important techniques in manufacturing semiconductor devices. The photolithography is able to transfer patterns from a mask to the surface of a silicon wafer; and form a semiconductor product that meets the designed requirements. During a photolithography process, by an exposure process, exposure light passes through the transparent regions of the mask to irradiate a photoresist layer on a silicon wafer. The photoresist has a photochemical reaction with the exposure light. Then, by a developing process, using the solubility difference between the exposed and non-exposed regions of the photoresist layer, photoresist patterns are formed; and a pattern transfer process is achieved. Then, the silicon wafer is etched using the photoresist patterns as an etching mask. The patterns on the mask are transferred to the silicon wafer.
During the exposure process, the mask has a certain degree of absorption to the exposure light. With the increase of the exposure time, the temperature of the mask is gradually increased; and the mask may be deformed by the heat. Accordingly, the overlay accuracy in the exposure region of the mask is affected. With the increase of the power of the laser in the photolithography apparatus, the effect brought by the heat-induced deformation of the mask has become more and more severe. Currently, the overlay accuracy deviation caused by the temperature change in the mask is up to 5 nm.
The overlay accuracy deviation may easily change the position and size of the finally formed semiconductor structure; and the performance of the semiconductor structure is easily affected. Thus, there is a need to reduce the heat-induced deformation in the mask during the fabrication process of the semiconductor structure. The disclosed structures and methods are directed to solve one or more problems set forth above and other problems in the art.